T1IK HEAD KIDNEYS. 



189 



diminishes in size. In 40 mm. tadpoles (Fig. 85) the head kidneys 

 are less than half their former size, and the tubules are completely 

 collapsed. By the time of the metamorphosis, the head kidneys 



AL 



RT 



OF 



RV 



KA 



KM 



LP 



TR 



FIG. 83. Diagrammatic figure of a 12 mm. Tadpole, dissected from the ventral 

 surface, to show the heart and branchial vessels, and the head kidneys and 

 commencing Wolffian bodies. The alimentary canal, from the resophagus 

 to the rectum, has been removed, x 22. 



A, aorta. AF.l, AF.3, afferent branchial vessels of first and third branchial 

 arches. AL, lingual artery. CGr, dilatation at the base of the lingual artery. EA, 

 communication between the afferent and efferent vessels of the first branchial arch, by 

 further elaboration of which the carotid gland will be formed. EF.l, EF.3, efferent 

 branchial vessels of first and third branchial arches. G-M, glomerulus. KA, segmental 

 duct. KM, Wolffian tubules. KP, head kidney. KS.l, first nephrostome. KS.3, 

 third nephrostome. LI, upper lip. L J, lower lip. LP, commencing hind limb. O A, 

 spout-like aperture of opercular cavity. OP, opercular cavity. RS, sinus venosus. 

 RT, truncus arteriosus. RV, ventricle. TO, cloaca. TO, oesophagus. TR, aperture 

 of rectal spout. 



have almost disappeared (Figs. 86 and 88), a few pigmented and 

 slightly twisted tubules alone remaining. 



All three nephrostomes disappear : the anterior one is the 

 first to close, and the middle one soon follows ; the third or most 



